1. Let’s Review… Copy in Notebook and Answer:
Compare and contrast magma and lava.
What plate boundaries will result in formation of a volcano?

2. What caused Mt. St. Helen’s to erupt?
Magma
What caused Mt. St. Helen’s to erupt?

3. How does Magma form? Magma is molten rock beneath the Earth’s surface
High Temperature:
Rocks melt at °C

4. Viscosity Viscosity – internal resistance to flow Low Viscosity
Moves fast (Less thick)
High Viscosity
Moves slow (More thick)

5. Types of Magma

6. Type of Magma Silica Content Gas Content Type of Volcano Example
Viscosity
Silica Content
Gas Content
Explosive-ness
Type of Volcano
Example

7. Hawaii Basaltic Low 1-2% 50% Least Shield Type of Magma Silica Content
Viscosity
Silica Content
Gas Content
Explosive-ness
Type of Volcano
Example
Hawaii
Basaltic
Low
1-2%
50%
Least
Shield

8. Hawaii Basaltic Low 1-2% 50% Least Shield Andesitic Medium 3-4% 60%
Type of Magma
Viscosity
Silica Content
Gas Content
Explosive-ness
Type of Volcano
Example
Hawaii
Basaltic
Low
1-2%
50%
Least
Shield
Mt. St.
Helens
Andesitic
Medium
3-4%
60%
Composite
Medium

9. Hawaii Basaltic Low 1-2% 50% Least Shield Andesitic Medium 3-4% 60%
Type of Magma
Viscosity
Silica Content
Gas Content
Explosive-ness
Type of Volcano
Example
Hawaii
Basaltic
Low
1-2%
50%
Least
Shield
Mt. St.
Helens
Andesitic
Medium
3-4%
60%
Composite
Medium
Cinder
Cone
Rhyolitic
High
Greatest
4-6%
70%
Yellowstone
*The higher the gas content, the more explosive the magma is going to be

10. Volcanic Material Tephra Pyroclastic Flow
Rock fragments thrown into the air during a volcanic eruption
Pyroclastic Flow
Rapidly moving volcanic material.
Speeds up to 200km/h
May contain hot, poisonous gases

11. Tephra
Pyroclastic Flow

12. Shield Volcano
Broad Gentle Sloping Sides
Non-Explosive

13. Composite Volcano
Alternates Lava and Tephra
Potentially most dangerous

14. Cinder Cone Volcano
Steep sides caused by tephra landing around vent
Explosive